1. Field of the Invention
This invention relates to combining the functions of an initiator, gas generator/heater and a "low pressure switch" (LPS) into a single device for convenience, termed herein an "initiator/monitor" device and having especial utility in the inflator of a vehicular stored gas inflatable air bag safety restraint system. A stored gas system includes a gas generator for the generation of gas and a vessel in which compressed or pressurized gas is stored to supply additional gas under pressure to inflate an inflatable air bag to protect the occupants of a vehicle upon the impact thereof with a harm producing object.
2. Description of the Prior Art
An inflatable air bag has a folded condition for storage in a steering wheel, dashboard or other appropriate location within a vehicle in close proximity to normal occupant position. Upon the occurrence of a collision of the vehicle, expansion of the inflatable bag may be effected or augmented by an inflator comprising a fluid supply in the form of a pressure vessel defining a chamber which contains a stored compressed or pressurized supply of gas.
In U.S. Pat. No. 5,290,060 granted on Mar. 1, 1994 to Bradley W. Smith entitled "HYBRID GAS GENERATOR FOR AIR BAG INFLATABLE RESTRAINT SYSTEMS" and assigned to the assignee of the present invention, a pressurized stored gas supply in a pressure vessel is released upon the actuation of a gas generator, more particularly, a pyrotechnic heater, which heats and increases the pressure of the stored gas. This causes the rupture of a portion of the pressure vessel which communicates with suitable gas flow directing means leading to and allowing the gas to escape into the interior of an inflatable bag. The bag inflates in front of the occupant and acts as a protective cushion.
The compressed or pressurized supply of gas is a very important part of a hybrid safety restraint system. If the gas pressure falls below a predetermined level, the system will not operate properly.
The pressurized vessel typically is compressed or pressurized with an inert gas such as argon, or a mixture of argon and another inert gas, to approximately 3000 psi at room temperature. Such vessels must be adapted to maintain the stored gas pressure so that the pressure does not drop by more than about 200 psi when at room temperature during the life of the vehicle which may be fifteen (15) years or more. These limits are illustrative only and are not intended in any manner to place restrictions on the scope of the claimed invention.
In a compressed or pressurized gas air bag inflation system, a means of predictably and substantially instantaneously releasing the pressurized gas from the inflator to fill the air bag is required. In addition, it may be desirable to heat the gas at the time of release to increase the pressure and/or improve the air bag inflation characteristics. Most domestic car manufacturers currently also require a temperature compensated means of detecting if a substantial amount of the compressed or pressurized gas has leaked from the inflator during the lifetime of the inflator.
Current hybrid air bag inflators use a "low pressure switch" to indicate the adequacy of the volume of gas stored in the inflator, an initiator (squib), a gas generator, and additional pyrotechnic material to heat the "cold" gas stored in the pressure vessel. There is a need and a demand for the replacement of the above components with one, cost effective, small device to reduce the complexity and cost of the inflator assembly. The present invention was devised to fill the gap that has existed in the art in this respect.